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Boron penetration through thin gate oxides in p-channel MOSFETs with heavily boron-doped gates causes undesirable positive threshold voltage shifts. P-channel MOSFETs with polycrystalline Si/sub 1-x-y/Ge/sub x/C/sub y/ gate layers at the gate-oxide interface show substantially reduced boron penetration and increased threshold voltage stability compared to devices with all poly Si gates or with poly Si/sub 1-x/Ge gate layers. Boron accumulates in the poly Si/sub 1-x-y/Ge/sub x/C/sub y/ layers in the gate, with less boron entering the gate oxide and substrate. The boron in the poly Si/sub 1-x-y/Ge/sub x/C/sub y/ appears to be electrically active, providing similar device performance compared to the poly Si or poly Si/sub 1-x/Ge/sub x/ gated devices.